It is known to coat medical devices, e.g. catheters for introduction into human cavities, such as blood vessels, digestive organs and the urinary system, with a hydrophilic coating, normally as a minimum applied on that part of the surface which is introduced or comes into contact with mucous membranes, etc., during introduction of the device. Whereas such a coating is not particularly slippery when dry it becomes extremely slippery when it is swelled with water, preferably immediately before introduction into the human body. The hydrophilic coating thus ensures a substantially painless introduction with a minimum of damage on tissue.
U.S. Pat. No. 3,967,728 to Gordon discloses the use of a sterile lubricant for deposition on and lubricating an uncoated catheter before use.
WO 86/06284 (Astra Meditech Aktiebolag) discloses a wetting and storing device for a coated catheter in which the coating may be wetted using water or water comprising common salt and possibly bactericidal compounds or other additives.
WO 94/16747 discloses a hydrophilic coating with improved retention of water on a surface, especially a surface of a medical device such as a urethra catheter, prepared by applying to the surface in one or more process steps at least one solution of components that will combine to form the hydrophilic coating. During the final step the surface is coated with an osmolality promoting agent, which is dissolved or emulsified in the solution or in the last solution to be applied when forming the hydrophilic coating.
Most prior art coatings are developed for instant swelling immediately before use of the medical device on which the coatings are applied.
It has been found, however, that most hydrophilic coatings lose their water retention and that the coefficient of friction increases when the coatings are stored in water for an extended period of time, particularly after sterilisation using irradiation or autoclaving.
It is described in EP 1 131 112 that the water retention can be increased dramatically and the initial coefficient of friction can be kept low by carrying out sterilisation of a medical device having a hydrophilic coating while in contact with an aqueous solution comprising hydrophilic polymers, for example polyvinylpyrrolidone or copolymers containing N-vinylpyrrolidone; poly[(meth)acrylic acid] or copolymers containing (meth)acrylic acid or (meth)acrylic acid esters; polyacrylamides; poly(vinyl alcohol) and copolymers of partially saponified vinyl acetate copolymers; poly(ethylene glycol); poly(vinyl methyl ether) or copolymers containing vinyl methyl ether, such as poly(vinyl methyl ether-co-maleic anhydride); copolymers containing maleic anhydride or maleic acid esters; or water soluble polysaccharides or derivatives thereof, such as carboxymethylcellulose (CMC) or hydroxyethylcellulose or xanthane or a derivative thereof. Thus, it seems that the hydrophilic polymers protect the above-mentioned properties during exposure to sterilisation using radiation when wetted with such a polymer solution.
However, there is still a need for methods for providing a sterilised medical device with a hydrophilic coating. Also there is a need for new ways of providing the hydrophilic polymer in a sufficient amount in the aqueous wetting liquid for the sterilisation to be carried out without detrimental effect to the water retention and the initial friction of the coating.